The invention relates to a swim fin, comprising a seat for the foot, the so-called footpocket and a propelling blade, the fin being composed of at least two materials, whereof one is comparatively rigid and substantially inextensible and the other is comparatively soft, i.e. has a different rigidity and/or is extensible.
Various types of fins having the above characteristics are known.
While these prior art fins have such a construction as to ensure a higher effectiveness as compared with traditional fins, they do not achieve an ideal hydrodynamic behavior. Moreover, during overmolding, it is often difficult to match and position the various parts the fin. In fact, the comparatively rigid parts of the frame are molded separately and then disposed in a mold for injection thereon of the additional material/s which complete the fin. In this step the various parts of the fin may easily be displaced relative to each other and/or to the surfaces of the mold.
Therefore, the present invention has the purpose to improve, by simple and inexpensive arrangements, a fin such as the one described hereinbefore, to achieve a better hydrodynamic behavior, closer to the optimum. Particularly, the aim is to diversify the rigidity and softness characteristics of the various parts of the fin, in order both to obtain an optimized transmission of the translational motion from the foot to the fin blade and to improve the hydrodynamic behavior of the blade. The fin shall have an inexpensive construction and allow to reduce and/or simplify the number of fabrication steps as compared with prior art fins of the same type. Another aim is a consistently safe and accurate positioning of the parts of the fin in the molding step.
The invention achieves the above purposes by providing a fin as described herein before, wherein the at least one comparatively rigid material forms the frame of the blade and/or footpocket. The part/s made of the at least one comparatively soft material may be then overmolded on the frame, which parts complete and/or connect and/or cover, at least partly, the various parts of the frame.
The comparatively rigid material which forms the frame may be a synthetic thermoplastic material, such as EVA or the like, whereas the comparatively soft material may be thermoset rubber or the like.
The frame made of the comparatively rigid material may include a pair of longitudinal members which form the cores of a pair of side frame members of the blade, said cores being arranged to be later covered, at least partly, by overmolding them with the comparatively soft material.
Advantageously, the cores of the side frame members may be provided with means for holding them in position inside the mold when they are overmolded with the soft material.
Said means for holding the cores in position may consist of at least a pair of parts projecting out of the surface of each core, which extend from diametrically opposite sides with respect to the longitudinal center axis of the core, and which are arranged to be clamped by the two mold and countermold parts when the latter are completely closed for soft material overmolding. Hence, any displacement of the cores relative to each other and/or to the two mold halves is prevented.
These retaining projections may be oriented in a direction substantially perpendicular to each blade face, i.e. to the parting plane between the mold and the countermold.
The retaining projections may be continuous and crest-like, and extend for at least a portion or for the whole longitudinal extension of each core, or be discontinuous and disposed in a predetermined arrangement over the length of each core.
The frame made of the comparatively rigid material may include at least a pair, but preferably a plurality of ribs which form more rigid and substantially inextensible blade parts.
The ribs may branch off from the cores of the side frame members and be connected thereto by being made of one piece therewith or by chemical and/or physical bonding, and are preferably made of the same comparatively rigid and substantially inextensible material.
The ribs may be at a distance from each other and each gap between each pair of adjacent ribs may be at least partly closed by a membrane-like element or the like, obtained by overmolding it with the at least one comparatively soft and/or extensible material.
The membranes which connect the adjacent ribs may advantageously be made of the same material used for covering the cores of the side frame members, such as thermoset rubber or the like, or of one or more different materials.
The ribs may extend from the cores of the side frame members up to the edges of a longitudinal median notch of the blade, which divides it into two half-blades.
Within each half-blade, the ribs may be substantially parallel.
The ribs may be disposed symmetrically with respect to the median longitudinal axis of the blade, i.e. with respect to the median longitudinal axis of the blade.
The ribs may be oriented toward the free end of the blade, so that each of them forms an acute angle with the portion of the side frame member included between the rib attachment area and the free end of the side frame member.
The ribs may preferably have a flat shape, and be all of the same length and/or thickness.
At least some of the ribs may have one or more upper and/or lower ribbed portions for further stiffening.
The membranes for closing the gaps between every pair of adjacent ribs may be equal or different in width to each other and/or to the ribs.
The closing membranes may have the same thickness as the ribs, so as to extend flush with both half-blade faces, or have a different, particularly lower thickness.
Advantageously, the closing membranes may have a bellows-shaped cross section, to improve the extensibility characteristics of the closing elements between the ribs.
Within each half-blade, at the free end portion thereof, there may be provided at least one end rib branching off the side frame member and extending to the edge of the free end of the half-blade.
In accordance with a preferred embodiment of the invention, the frame made of the comparatively rigid material may also include a footpocket frame, which may be steadily connected to the cores of the side frame members by being made of one piece therewith or by chemical and/or physical bonding. The footpocket may be further completed by overmolding it with one or more parts made of a comparatively soft material.
These parts made of a comparatively soft material, which complete the footpocket, may include the portion in contact with the instep and/or an inner comfortable cover and/or non-slip members at the lower face of the footpocket and/or additional parts, such as a fastening strap made of one piece with the footpocket.
Advantageously, the frame of the footpocket may itself have one or more projections for locking it in position, which cooperate with the surfaces of the two mold parts when the latter are closed, in the same manner as described above for the side frame members and still aimed at preventing any relative motion of the parts of the footpocket in the molding step.
In accordance with a preferred embodiment of the invention, the whole frame of the fin may be made of a single material, or the frame of the footpocket may be made of one or more materials differing from the material/s of the cores of the side frame members and/or of the ribs.
Also, according to a preferred embodiment, all the comparatively soft parts of the fin may be made of a single material, wherewith the frame is overmolded, or two or more different materials may be provided.
The frame of the footpocket may extend at and form the bottom wall of the footpocket, so that the latter may be stiffened in a highly stressed portion.
According to a preferred embodiment, the frame of the footpocket may also extend in the upper portion of the foot, and create a seat which surrounds substantially the whole foot, to obtain an optimized transmission of the translational motion from the foot to the blade.
The advantages of the present invention are clearly shown by the above description and consist in the possible improvement of prior art fins of the same type, by using simple and inexpensive arrangements, to obtain a better hydrodynamic behavior. Thanks to the characteristics of the fin of this invention, an optimized diversification of the rigidity and softness characteristics of the parts of the fin may be achieved. In some types of prior art fins, this diversification is typically obtained by thickness variations of the fin parts, a single material being used in the whole fin, wherefore the result is never optimal. The fin of the invention is inexpensive as regards construction and allows to reduce and/or simplify the number of fabrication steps as compared with prior art fins of the same type. In fact these typically include several elements made of a comparatively rigid material which are to be joined together and with the comparatively soft parts, whereas the preferred embodiment of this invention advantageously includes a frame formed by a single element, which may be molded in one step and joined to the other parts by a single additional overmolding step. Moreover, thanks to the locking projections on the cores of the side frame members and/or in the shell of the footpocket, the parts of the fin may be always positioned in a safe and certain manner, particularly the comparatively rigid parts with respect to the comparatively soft parts. Yet a further advantage consists in a reduced use of the comparatively soft material, typically thermoset rubber or the like which is known to be a rather costly material, compensated by an increased use of the comparatively rigid material, typically a thermoplastic material or the like, which is known to be a less expensive material, whereby the total fabrication costs of the fin are lowered, without affecting the functionality thereof.
Referring to another characteristic which may be provided in any type of fin having a blade composed of two half-blades or of two half-wings separated in the median area at least partly by a longitudinal notch, the half-blades or the half-wings bear elements on one, on the other or on both faces to control bending in one, in the other or in both bending directions of the half-blades or wings.
Advantageously these control elements consist of control notches which cooperate with longitudinal ribs, especially with the side frame members of the blade.
An additional improvement provides that the bending control notches or abutments are positioned, or have surfaces that limit abutment, against the longitudinal ribs, particularly the side frame members of the blade to define, at the end of the bending stroke of each blade part or of each wing, a particular bending shape, especially an approximately helical shape.
In combination with the fin of the above description, the control notches or abutments are borne by the ribs integral with the core of each side frame member.
Thanks to this arrangement, not only is a precise deformation of the half-blades or of the wings obtained in the maximum bending condition but, by avoiding excessive bending deformations and by always keeping deformations well defined in terms of shape, the stress of the material is limited and the fin has a longer life.
Further characteristics and possible improvements of the invention will form the subject of the dependent claims.
The characteristics of the invention and the advantages derived therefrom will be more apparent from the following detailed description of a preferred embodiment shown in the annexed drawings, in which: